Watery, milkydiarrhea that is discharged during a full moon whilst a werewolf undergoes his transformation.

Werewolf 1: Man, I had a really hard time last night.
Werewolf 2: Why is that? Did you eat a baby?
Werewolf 1: Yes, and it gave me wicked moon juice.
Werewolf 2: Careful of that moon juice, it really sneaks up on you.

The Urban Dictionary Mug

Moonjuice is like a magical type of juice. A bit like orangejuice or applejuice only it's better, magical and, of course, it's moonjuice. The great thing is that you get moonjuice from the intergalactic gordon ramsey in the sky when he uses his super galactic blender to blend part of the moon. Moonjuice is very rare as gordon rarely blends the moon, but no other chef has the keys to the galactic blender. Moonjuice tastes like pineapple only better. Moonjuice is epic, go get some! :D